Developing renewable sources of feedstocks based on biomass for making distillate products, such as fuels or lubricants, is an area of ongoing interest. Use of biomass as a feedstock source is attractive from a perspective of avoiding depletion of mineral oil and gas sources. However, a variety of challenges remain in developing technologies for harvesting and processing feeds derived from biomass.
In addition to the challenges for making fuels from feeds derived from biomass, production of lubricant base oils from renewable sources poses additional problems. One difficulty is that renewable feeds are typically more likely to contain molecules with chain lengths and/or molecular weights corresponding to the diesel boiling range. For example, fatty acids present in some types of biomass typically have carbon chain lengths of 20 atoms or less, which usually corresponds to a diesel boiling range molecule. Biomass feeds with molecules having chain lengths in the lubricant base oil boiling range are currently less common. One option for making a lubricant base oil product from a feed containing fatty acids is to couple two or more fatty acid chains to create molecules with longer chain lengths.
European Patent Application No. EP 0457665 describes performing a condensation reaction on carboxylic acids or polyfunctional compounds such as triglycerides using a catalyst based on an iron-containing mineral, such as bauxite.
U.S. Pat. No. 8,048,290 describes a process for producing branched hydrocarbons. A feedstock derived from a biological starting material, such as a fatty acid or a fatty acid derivative, is subjected to a condensation step to produce hydrocarbons that also contain one or more heteroatoms, such as oxygen or nitrogen. The condensation product is then subject to a combined hydrodefunctionalization and isomerization step. In this combined step, isomerization and heteroatom removal are performed in the same step. Examples of suitable catalysts for performing the combined hydrodefunctionalization and isomerization step include alumina bound ZSM-23 or SAPO-11 with supported Pt as a hydrogenation metal. ZSM-48 is also mentioned as a suitable zeolite.
U.S. Pat. No. 8,053,614 describes a method for producing a base oil. In various options, triglyceride containing feeds are converted to fatty acids or fatty acid alkyl esters. The fatty acids or fatty acid esters are then used to form ketones via a m condensation reaction. The ketones are then deoxygenated in a hydrogenation step to form paraffins, which were then isomerized. One or more distillation or separation steps are included at various points in the process of converting the triglyceride containing feed to the isomerized paraffin.